Watershed Delineation using ArcGIS from DEM - Simple and Straightforward

hi welcome to another tutorial on our GIS today I will show you how to delineate a catchment using a DM with the help of ArcGIS as our primary GIS tool so first of all you can see that I have loaded up my de M if you would like to know how to download a de M I have already prepared a tutorial for that and I will I will put the link in the description below you can first study that tutorial how to download an ester de m from the NASA website and here you can see that I have already loaded up the TM into our GIS interface so for this tutorial I will be using the hydrology toolbox which actually comes in built with ArcGIS so the first thing that you would need to do is after you load the de M you will have to go to the arc toolbox and under spatial analyst tools you will see that this option called hydrology so before we are actually able to use this tool first of all you need to go to customize and under extensions you will see that you have some unchecked unchecked extensions in case if you have already checked it and all of these extensions then you're good to go but in case if you haven't you especially need to have this spatial analyst extension activated for the for the process that we are going to do today so after you activate that I'm going to click OK close after we download the de M we have to actually fill the sinks so first we need to click on this field just double click and as the input surface roster you're going to put the rhodium that you downloaded from from the website so you just drag this and drop and for the output surface roster you can actually specify the output location but for for now I'm just going to leave it as it is and click OK so what happens in this step is actually if there are any sinks present in the in the rhodium this algorithm will actually fill up those things so that we can proceed with the with the next steps that we need to do so as you can see we already created a field TEM the next step would be actually now you can see that you have to to rust as the first one is the rhodium that we already had before and now you have a filled DM so I'm just going to uncheck this one because we won't be needing that anymore and the next thing that you need to do is actually you need to create a flow Direction roster so after fill the second step would be to create a flow Direction roster so you double click on this one and as the input to this one we should put the filled DM not the rhodium so you just drag this one and drop it over here and I will correct the name just to just to make it a little bit clearer flow direction and press ok so it might take some time to create the flow Direction roster and you see that we already have the flow Direction roster now now what does this different colors indicate as you can see over here under the flow Direction roster you see a few numbers 1 2 4 8 16 32 64 and 128 so just before going into the next step I would like to give you some idea about this flow Direction roster and if you just wonder what these numbers mean I would just quickly explain to you what exactly these numbers mean now here I have actually come to the help of rjs and it says how does the flow Direction works and here and here I would like to bring to your attention this direction coding as you can see these different colors and different numbers indicate directions so one is actually to the to the to the eastern side and 16 is to the western side and 64 is actually to the northern side and 4 is to the southern side and like so so if you just come back to the flow Direction roster you created and if i zoom in a little bit you can see that these individual pixels actually take the color which is represented by each of these colors which also has the number which explains you actually the direction of the flow so that's actually the meaning of this flow direction roster so our next step would actually be to create the flow accumulation roster so after we guide the flow to has its own direction based on the topography the next step is actually we need to see the flow accumulation points so you just double-click on the flow accumulation and as the input for this one we just drag and drop the flow Direction roster and as the name of the accumulation roster just give the name to be flow sec and click OK alright now you can see that our flow accumulation roster is complete but it's not actually quite visible yet unless we do some modifications in the symbology so what I'm going to do here is just going to click on the flow accumulation rustin i'll just uncheck these because we won't be needing them for the time being and you go to properties of the flow accumulation roster and go to symbology and instead of using a stretched option let's use X let's use a classified option and by default you can see that the number of classes that it gets classified to is 5 but I'm going to change this to 2 and I will explain you the reason why and you can see actually now we are classify we are trying to classify the whole thing into two two colors so let's go to classify and instead of having such a broad range for black color as you can see over here I'm going to assign in a way that it will show us in black color the accumulations which are quite small from zero let's say up to 25,000 and click OK so from 0 to 25,000 which corresponds to actually very low accumulations it will be represented in black color and on top of black since white is going to be quite easily visible I'm going to leave the rest of the accumulations to be in white color now when I click apply you can see actually all the flow accumulations which corresponds to which correspond to this this particular range it's very easily highlighted now if you decide to go a little bit low on this number for example instead of going a 25,000 if I were to put just 1000 and click OK you can see it actually starts showing us all this all the very localized accumulations as well instead of showing the the main river lines and if you zoom in you can see that all the sub reaches are also now visible but this is this looks a little bit messy and I'm interested in only having the the major river lines highlighted so I'm going to stick with let's say around 25,000 and the rest I would like to represent that in white color so for this example let's assume that I need to have my catchment outlet somewhere over here and I would like to know what is the the the corresponding contributing drainage area for that that particular outlet from this particular sub catchment so what I'm going to do is first I need to create a new shapefile and define my define the exact location of my outlet and make sure that that outlet point is located exactly on top of this cell but not outside the range of this this white color cells so in order to do that you have to create a new shapefile and there's there's also another tutorial where I have explained you how to create a new shapefile but I will explain to you again first you go to catalog and you select the place where you need to save your new shapefile so let's say if I would like to save it over here you have to right-click and go to new and a new shapefile and I'm going to call this s outlet of the catchment and the future type is going to be a point and here it's quite important that we define the correct projection system and for this tutorial I am using the 1984 geographic coordinate system so I'm going to select that WGS 1984 and click OK right now we are almost ready to create our shapefile now let's go to this editor and click start editing and click outlet catchment ok go to editor again editing windows create features I'm going to get rid of the arc tool box and click on this outlet catchment and under the construction tool you have to select point and as you can see since I'm trying to identify the contributing drainage basin for this particular River branch I'm going to zoom in to the point where this river connects to the main river and I'm going to place my point somewhere over here ok that's done let's go to editor and click stop editing and save your edits ok now you can see you have your point which we call as a pour point now get rid of this create features panel and now we have to go with this watershed option double click on the watershed option and as the input you have to drag and drop the in the flow Direction roster and here it's asking us an input roster or a feature for point data so we already created the pour point data and our pour point is actually the catchment outlet so I'm going to track this one and drop it over here and click okay now I'm going to zoom it out so when it creates the catchment it will be easily visible for you all right now you can see that we already created the the catchment and it shows us actually the contributing area for this catchment outlet point based on this DM right and right now this catchment is actually still in the format of a raster if you go over here and if you open the attributes table you can see that is actually in the form of a roster for other analysis purposes normally it's required that you convert this raster into a polygon so you can do other analysis such as calculating the area or based on your requirements so what we do over here is we go to the search panel and we search raster to polygon and you can see and as you can see the first option is converting converting a roster into a polygon so I'm going to drag this raster and drop it over here and now and now I think it's clear for you that this raster corresponds to the roster which got generated based on the topography of the DM and I'm going to simplify the polygons as well what this does is actually in the in the at the edges of the catchment if you do not unseen Riis of the of the pixels in sort of rectangular format but if you click on this one it'll sort of simplify the polygons as well so and then click OK alright now you can see you successfully created your first watershed so that's about it for this tutorial and here I showed you how to create one watershed but but in case if you need to create multiple watersheds at one time you don't have to do this process over and over again there is another easy quick and an easy way and I will show you how to do that in the next tutorial thank you

Channel: GeoDelta Labs

Views: 22,958

Rating: 4.9643917 out of 5

Keywords: Watershed delineation, ArcGIS, ArcMap, QGIS, How to, demarcate, catchments, hydrology, GIS, ModelBuilder, DEM, NASA, ASTER, Digital Elevation Model, Sub-catchment, Basin, River

Id: v3Ajg6W8Rj8

Length: 13min 13sec (793 seconds)

Published: Tue Feb 05 2019